Pump selection: Is it really this simple?

[combatwombat]

Hello pond geniuses!

My excavator called this morning and said he wanted to come start digging... tomorrow! I thought I'd have more time to figure some details out, but this is a good kick in the pants to get my plans in place today.

Long story short: I am estimating my new water garden to be about 7,000-7,500 gallons (probably less, actually, once you figure in all the boulders?). For a pond this size, I am thinking 50% turnover per hour, so about 3,500gph pump needed.

An upflow bog filter that is about 15% of pond surface area will be the only filtration (for now at least). It will be located roughly 90' from the pump and 3' above the pond's water level and will have a ~35' step pool stream that is 2-3' wide flowing back to the pond from the bog. I am not overly concerned with having epic waterfall type flow through the stream.

From the millions of words I've devoured here about bog filtering, it sounds like you can send just about any gph you want through a bog and it will do it's job.

So, I'm thinking all I need to do is find a pump that can do roughly 3,500gph at 12' head pressure (90' of 2" pipe + 3' of grade change = 12' head pressure), send it all to the bog, and let gravel, bacteria, and gravity do the rest.

Am I on the right track here?

If you're wondering "why do you need to know pump size for excavation?", it's because I'm digging an intake bay, and I want to make sure I get the intake bay sized right for the size of pump I need.

As a precaution, I'll probably plan to just dig it bigger than necessary and I think there's no harm in having an intake bay that's too big.

Thank you all so much for whatever help you can offer.

 

[TheFishGuy]

I cant give nay advice on the bog side of things, but will say the brand ( really just quality ) is very important. I have two pumps: one an 800 gph and one a 1200 gallon per hour. the 800 cost me 25 bucks, while the 1200 cost me 200. While this may seem like a lot, down the road because of its solids handling and all that I only have to clean it once a season, while my other pump I have to clean EVERY day.

I would really recommend aquascape, they are expensive but amazing!

 

[mrsclem]

You don't say if you are planning on fish. Guessing you are so the turnover rate needs to be 1 1/2- 2 times per hour so 10,000-14,000 gph.

 

[combatwombat]

Thank you @TheFishGuy & @mrsclem.

@mrsclem: We are not planning to have fish at first. But I would like to size things so that we can have a light goldfish load down the road. I know how that can balloon for some people into overstocked koi ponds, but I don't think that'll be us (famous last words).

Does the 1.5-2x turnover apply to ponds of this size with a light load? I am completely new pond keeping, but I thought that turnover rate drops off as your pond gets bigger. Pumping 14k gpm sounds bonkers!

 

[TheFishGuy]

Thank you @TheFishGuy & @mrsclem.

@mrsclem: We are not planning to have fish at first. But I would like to size things so that we can have a light goldfish load down the road. I know how that can balloon for some people into overstocked koi ponds, but I don't think that'll be us (famous last words).

Does the 1.5-2x turnover apply to ponds of this size with a light load? I am completely new pond keeping, but I thought that turnover rate drops off as your pond gets bigger. Pumping 14k gpm sounds bonkers!

pumping 14k gallons per hour does sound pretty crazy! Again, I wont interfere with an experts advice though....

 

[mrsclem]

With no fish load you can go with the 3500gph. Just figured with the size, you were planning on fish. My bad! I'm one of those overstocked koi pond owners!

 

[combatwombat]

With no fish load you can go with the 3500gph. Just figured with the size, you were planning on fish. My bad! I'm one of those overstocked koi pond owners!

Thanks for clarifying! I think I will probably put some safety margin into the sizing. Maybe bump it up to 4500 - 5000 because I know that once we have 1 goldfish, it will probably spiral out of control until we're commercial tilapia farmers or something.

 

[j.w]

@combatwombat

 

[Jhn]

I would size the intake bay to handle 1.5-2x per hour pond turnover. Even if you go with the smaller pump initially, because once you add fish even a few, your pond will be overloaded with them eventually. Which in turn will require an upsizing of your pump. Under shooting your pond circulation even in a lightly stocked pond can cause algae problems as there will be dead spots in the pond where plant debris/mulm/ waste will accumulate.

Really will depend on how well you can eliminate dead spots and circulate Water around The pond in your design. The bog will definitely prevent this from occurring for awhile, but my thoughts are plan on the pond being overstocked at some point in the future.

 

[combatwombat]

I would size the intake bay to handle 1.5-2x per hour pond turnover.

Duly noted. Great point. Honestly, as cool as intake bays are, I am thinking I might go back to just using a skimmer. It's a lot simpler to design! I better make a decision because my excavator is coming tomorrow...

 

[poconojoe]

Considering the size of your planned bog....I think you stated your bog surface is planned to be 15% of the pond's surface. From what I have read, that should be fine if you have little or no fish load, but if it becomes overpopulated or you're keeping koi, the suggested percentage bumps up to 30%.

That being said, I can tell you from experience that your fish will multiply and your pond will quickly become overpopulated. It may take a couple seasons for them to start breeding, but when they do....the population grows quickly.

My bog is slightly over the 30% mark and it is amazing.

So, think about it....it's up to you.

Oh, I'm using a Tetra debris handling pump that is a little over 3,600 gallons per hour and it seems perfectly sized for my approximately 1800 gallon pond and 14 foot x 5 foot x 12 inch deep bog. I'm no expert on pumps, but you state 3,500 for a 7,000-7,500 gallon pond. I don't know....maybe you should do more research, that size pump seems a bit small. Hopefully the experts here can chime in and correct me if I'm wrong.

Good luck, keep us posted on you progress and throw up some pictures when you get underway.

 

[JamieB]

An alternative to buying a big pump is to have two smaller ones, so two that are roughly the gph of your pond volume. It’s something I’ve been thinking of, as a “ just in case”, one goes down, you’ll have one this still moves water.

 

[brokensword]

I second what Jamie recommends; two are safer than one, though you'll need more plumbing pieces. I often refer to what Meyer Jordan once told us and his recommendation re flow through the bog is that the plants and bacteria are more able to take up the nutrients if they get more time to do so. That said, I also think you can create some channeling easier with a flow that is too swift/much, so perhaps think of dividing your pumps such that one goes to your bog and one goes to a waterfall for additional aeration? Gives you more options, this way.

And in my case, I have two 4k gal/hr pumps for a 7000 gal overstocked pond and haven't had any issues. I second PJ's thought to make your bog surface larger/as large as you can; you'll thank him later.

Just a thought or two.

 

[combatwombat]

@poconojoe: All good points. I've been wondering about what you do when you want 5 goldfish and end up with 500. I will make the bog as big as I possibly can. Might be able to squeeze a bit more area out of the space I have planned for it. Also might use @JamieB and @brokensword's advice to split into two pumps and send one of them to a biofalls so that I get a backup pump and can ramp down the gpm to the bog for more dwell time. Also, more waterfalls are more awesome, I guess.

This project was a bit expensive to begin with, and now it's getting even worse. I do love over-engineering, though.

 

[JamieB]

You know, I’ve got to ask, are you ausi military? With a name like yours, that’s my first thought!